The present invention relates generally to a Radio Frequency Identification (RFID) device having a nonvolatile ferroelectric memory, and more particularly, to an RFID device which senses the off period of a radio frequency signal regardless of the power voltage in order to generate a stabilized power-on reset signal.
The data processing speed of nonvolatile ferroelectric memory, that is, Ferroelectric Random Access Memory (FeRAM) is typically similar to that of Dynamic Random Access Memory (DRAM). However, FeRAM is different from DRAM, in that data stored in FeRAM is conserved even when the power supply of the memory device is turned off. Thus, FeRAM is quickly gaining publicity and is considered a strong candidate as a next generation memory device.
The structure of FeRAM is similar to that of DRAM, in that FeRAM includes a plurality of capacitors. However, the capacitors in a FeRAM device are made of a ferroelectric material having a high residual polarization, which in turn allows for data retention even when the power supplied to the memory device is terminated.
In a device which utilizes nonvolatile ferroelectric memory as a memory device, a system controller outputs a chip enable signal to the nonvolatile ferroelectric memory chip. In response to the chip enable signal, the memory device included in the memory chip generates a chip internal control signal for operating the memory cell of the chip. Data are read from or written to the memory cell in response to the chip internal control signal.
The device utilizing the nonvolatile ferroelectric memory reads data stored in a code register when a power source is applied to the nonvolatile ferroelectric memory in order to “set up” the data. The read operation of the code register is performed in response to a power-on reset signal.
Conventional power-on reset circuits are configured to generate a power-on reset signal using the power voltage. That is, when the power voltage is changed from off to on, the power-on reset signal is generated.
If the power voltage drops below a threshold, the power-on reset circuit recognizes the power voltage as off. In order to compensate for this problem, the power source must be stabilized, so that a level of the power voltage does not drop if an off period of the power voltage is not sufficiently long.
However, when the power voltage is changed from off to on for a short period of time, the power-on reset circuit does not generate the power-on reset signal. As a consequence, the power-on reset operation is not performed normally.